Towards a marginal Arctic sea ice cover

最近观察到的北极变化已成为全球气候变化的典型，特别是因为夏季海冰面积在过去35年里迅速缩小。海冰的这种消退导致了跨北极航运的增长，并计划从海底开采矿物和化石燃料。政府间气候变化专门委员会(IPCC)的最新评估得出结论，假设温室气体排放继续增加，北极很可能在2050年变得可靠地无冰。然而，IPCC使用的气候模拟往往无法真实地捕捉北冰洋海冰的大范围特性，如范围、变化性和最近的趋势。因此，有必要改进北冰洋海冰的模拟，以便更好地了解最近观察到的变化和对未来的可信预测，以帮助评估风险和机会，并为有关适应和缓解的重要决策提供信息。近年来，随着从太空测量海冰特性的新卫星的出现，对北极的观测有所改善。这些卫星不仅揭示了北极冰盖的范围和厚度在所有季节都在减少，而且边缘冰区(MIZ)--一个由相对分散的小浮冰组成的低冰区集中区--正在增长。模型预测表明，到2050年，MIZ将从夏季海冰覆盖的10%左右增加到80%，使迄今相对平静的北冰洋暴露在大气中。空气、冰和海洋之间的非线性相互作用放大或减小变化，称为反馈，与缩小和边缘的海冰覆盖有关，将在未来几年出现或占据主导地位。这些反馈中的许多要么完全不存在，要么在当前模型中没有得到充分的捕捉。例如，没有包括这样的反馈，即在海浪压力下，由于冰的融化或破裂而产生的较小的浮冰促进了进一步的横向融化和波的传播，使MIZ进一步扩大。由于现有的气候模型过度简化了这些反馈，它们在理解和预测北极的可变性和变化方面的效用受到了影响。由于经向大气和海洋环流的误差以及北极冰的输出，这也导致低纬地区气候模型的准确性受到损害。我们将利用现有的和新的观测资料来研究控制MIZ演化的过程。我们将包括波浪-冰相互作用的物理学，冰的破裂和融化，以及浮冰与冰、海洋和气候模型的碰撞。我们将使用这些受新观测约束和验证的模型，通过一系列数值实验来探索海冰、海洋和大气之间的反馈。我们将量化MIZ增加对北极物理气候的影响，并探索导致北冰洋海冰预计消失的过程。

Recent observed changes in the Arctic have become a 'poster child' for global climatic changes, particularly because the summer sea ice extent has shrunk rapidly over the past 35 years. This retreat of the sea ice has led to growth of trans-Arctic shipping and plans to extract minerals and fossil fuels from the ocean floor. The latest assessment of the Intergovernmental Panel on Climate Change (IPCC) concluded that it was likely that the Arctic would become reliably ice-free by 2050 assuming greenhouse gas emissions continue to increase. However, the climate simulations used by the IPCC often fail to realistically capture large scale properties of the Arctic sea ice, such as the extent, variability and recent trends. Therefore, there is a need to improve simulations of Arctic sea ice to provide better understanding of the recent observed changes and credible projections of the future to help assess risks and opportunities and inform important policy decisions about adaptation and mitigation. Observations of the Arctic have improved in recent years with new satellites measuring sea ice properties from space. These satellites reveal not only that the extent and thickness of the Arctic ice cover is reducing in all seasons but that the Marginal Ice Zone (MIZ), a region of low ice area concentration consisting of a relatively disperse collection of small floes, has grown.Model projections indicate the MIZ will grow from around 10% to 80% of the summer sea ice cover by 2050, exposing a hitherto relatively quiescent Arctic Ocean to the atmosphere. Nonlinear interactions between the air, ice, and ocean that magnify or diminish change, known as feedbacks, associated with a reduced and marginal sea ice cover will emerge or assume dominance in the coming years. Many of these feedbacks are either entirely absent or inadequately captured in current models. For example, not included is the feedback whereby the creation of smaller floes due to ice melt or breakup under ocean wave stress promotes further lateral melt and propagation of waves deeper into the pack, further enlarging the MIZ. Because existing climate models oversimplify these feedbacks, their utility for understanding and predicting variability and change in the Arctic is compromised. This leads to impairment of climate model accuracy at lower latitudes also, due to errors in meridional atmospheric and oceanic circulations as well as ice export from the Arctic. We will investigate processes controlling evolution of the MIZ using existing and new observations. We will include physics of wave-ice interaction, ice breakup and melt, and floe collisions into ice, ocean, and climate models. We will use these models, constrained and verified with new observations, to explore feedbacks between the sea ice, ocean, and atmosphere using a series of numerical experiments. We will quantify the impact of the increase in the MIZ on the Arctic physical climate, and explore the processes responsible for the projected loss of Arctic sea ice.